MBR disk dual boot messed up, SL and Vista

I've had Snow Leopard and Vista dual booting for awhile, but I messed it up yesterday. I went to edit Vista's BCD with the BCDEdit command-line tool, but I got an error. Google said I needed to to set my Windows partition as active so I used the Windows Disk Management tool. But when I restarted the computer PC EFI didn't load. So I used the Windows Disk Management tool to set my SL partition as active...hence my problem.

Now PC EFI loads in GUI mode (before it loaded in non-GUI) with two options: Windows and Windows NTFS. The first loads Vista and the second (presumably SL) loads a black screen with a blinking cursor.

If I use the Windows Disk Management tool to set the Windows partition as active, it goes straight to windows. I booted into the SL install disk and used fdisk to set the SL partition as active. But I get the PC EFI same as described before.

I also tried to 'Repair Disk' from the Disk Utility on the installation disk and I get an error saying it failed the file system validation (because it thinks it's NTFS but it's actually HFS+).

The disk is MBR.

Is there a way for me to fix my problem? A tool to repair the partition or partition map?

I have an extra partition if it would help to have another installation of OS X to work from.

I also posted this question at insanelymac ↗.